HTC One E8 - Manual (Page 52)

Other tips
To squeeze in a little bit more battery power, try these tips:
§ Tone down the ringtone and media volume.
§ Minimize the use of vibration or sound feedback. In Settings, tap Sound and
choose which ones you don't need and can disable.
§ Check your apps’ settings as you may find more options to optimize the battery.
52 Your first week with your new phone